The present invention relates to a steering apparatus for automobiles for directing steerable wheels by a steering mechanism which is not mechanically connected to a steering operating means according to an operation by an operator.
An automobile is steered by transmitting an operation of a steering operating means (in general, rotation of a steering wheel) provided in a vehicle chamber to a steering mechanism provided outside of the vehicle chamber so that steerable wheels (in general, front steerable wheels) for steering are directed.
As the steering mechanism for automobiles, various mechanisms such as ball-screw type and rack-pinion type mechanisms are put to practical use. For example, in the rack-pinion type-mechanism they are arranged so that sliding of a rack shaft which is extended in the right-and-left direction at the front portion of the body of a car, in a shaft-length direction is transmitted to a knuckle arm provided to right and left front steerable wheels via a tie rod. In this mechanism, a pinion fitted into a top end of a rotation shaft (steering column) of a steering wheel extended on the outside of the vehicle chamber is engaged with a rack gear disposed in a midway of the rack shaft, and the rotation of the steering wheel is converted into sliding in the shaft-length direction of the rack shaft so that steering is performed according to the rotation of the steering wheel.
In addition, in recent years, a power steering apparatus is spread widely. Such power steering apparatus is arranged so that actuators for helping steering such as a hydraulic cylinder and an electric motor are provided in a midway of the steering mechanism, the actuator is driven on the basis of a detected result of a steering force applied to the steering wheel for steering, and an operation of the steering mechanism according to the rotation of the steering wheel is assisted by an output of the actuator, and thus driver""s effort at steering is reduced.
However, in such a conventional steering apparatus, since the steering wheel is connected mechanically to the steering mechanism regardless of the provision of the arrangement as a power steering apparatus, there arises problems such that a position in the vehicle chamber where the steering wheel is placed is limited, and that a degree of freedom of a layout in the vehicle chamber is restricted. Moreover, the realization of the connection requires large-bulk connecting members, and thus realization of lightening of cars is obstructed.
In order to solve such problems, there is suggested a separation-type steering apparatus which is arranged so that the steering wheel as steering operating means is not mechanically connected to the steering mechanism, meanwhile similarly to the actuator for assisting the steering in the power steering apparatus, the actuator for steering is provided in the midway of the steering mechanism, the actuator is operated on the basis of a detected result of an operating direction and operating amount of the steering operating means, thereby applying a steering force to the steering mechanism, the steering is thus performed according to the operation of the steering operating means.
In addition to the advantage of solving the above problems, the aforementioned separation-type steering apparatus has an advantage that since a relationship between an operating amount of the steering operating means and an operating amount of the steering actuator can be set without any mechanical limitation, it can cope with the change of steering characteristics according to a running state of an automobile such as the speed, a degree of turning, and an increase and decrease in the speed flexibly, and suitable steering operating means such as a lever, hand grip and pedal can be adopted instead of the steering wheel, and a degree of freedom of design is improved.
Further, the separation-type steering apparatus has an advantage such that rising of the steering wheel due to a head-on collision of an automobile can be prevented substantially completely, safety in a collision can be improved, and this apparatus can easily cope with automatic driving systems such as ITS (Intelligent Transport Systems) and AHS (Automated Highway Systems) which are being developed in recent years. Namely, the separation-type steering apparatus has a lot of advantages which cannot be realized in the conventional steering apparatuses, so it is watched with interest as an useful apparatus for developing automobile technique.
Here, as the steering actuator for applying a steering force to the steering mechanism, considering the ease of changing the steering characteristic according to the running state, an electric motor (steering motor) is generally used. Moreover, the steering operating means separated from the steering mechanism is provided with reaction force applying means having a motor and a gear mechanism, and when the reaction force applying means applies a suitable reaction force to the steering operating means, it can perform the steering operation in like a manner in the apparatus where the steering operating means is mechanically connected to the steering mechanism.
When the separation-type steering apparatus having the above arrangement is compared with the power steering apparatus used widely, the steering in the latter apparatus is performed by the combined force of an operating force applied to the steering wheel as the steering operating means and an output of the motor for helping the steering provided to the steering mechanism, but the steering in the former apparatus is performed only by an output of the steering motor provided to the steering mechanism.
Therefore, as the steering motor used in the separation-type steering apparatus, compared with the motor for helping the steering used in the power steering apparatus, higher-powered motor is required, so there arises a problem that it is difficult to secure a position, where the large-size steering motor according to the large power is placed, in the vicinity of the steering mechanism.
Further, if the motor for assisting the steering breaks down in the power steering apparatus, since only a steering helping power is lost, the steering can be performed by the operating force applied to the steering wheel, but if the steering motor breaks down in the separation-type steering apparatus, there is a possibility that the steering becomes difficult.
The present invention has been devised to solve the above problems. It is an object of the present invention to provide a separation-type steering apparatus for automobiles which easily secure a position in the vicinity of a steering mechanism where a steering motor is placed, and can previously prevent steering from becoming difficult even if the steering motor breaks down.
The steering apparatus for automobiles according to the present invention is characterized by including steering operating means which is not mechanically connected to a steering mechanism, a pair of steering motors provided to different positions in the steering mechanism, and a steering control unit for distributing a necessary steering force obtained on the basis of a deviation between an operating position of the steering operating means and actual operating position of the steering mechanism in a prescribed ratio so as to determine target value of the outputs of the steering motors. Since a combined force of a pair of the steering motors is applied to the steering mechanism to perform the steering, both the steering motors can be miniaturized, and thus their provision to the circumference of the steering mechanism becomes easy.
In addition, the apparatus is characterized in that the steering control unit includes means for judging as to whether or not malfunction exists in said steering motors and the relevant electrical and mechanical part thereto, and fail-safe means for changing the distribution ratio so that an output of the steering motor on a malfunction side is forbidden according to the judgment and the output of the steering motor on the non-malfunction side is increased. As a result, when one of the steering motors malfunctions, the operation of the malfunctioned steering motor is forbidden by changing the distribution ratio according to the judgment of the malfunction, and the output of the steering motor on the non-malfunction side is increased, and the steering can be performed by one steering motor.
In addition, the apparatus is characterized in that the steering control unit obtains a normal output according to the distribution ratio and a fail output corresponding to the whole of the necessary steering force for each of the steering motors, and the fail-safe means changes the normal output into the fail output for the steering motor on the non-malfunction side. As a result, the fail output corresponding to the whole of the necessary steering force is obtained for each of the steering motors during the normal operation, and if one steering motor malfunctions, the target value of the output of the other steering motor is changed into the fail output so that this steering motor immediately generates the whole of the necessary steering force shared by a pair of the steering motors before the malfunction, and thus an abrupt change in the steering force due to the changing can be prevented.
The above and further objects and features of the invention will more fully be apparent from the following detailed description with accompanying drawings.